Optical communications systems utilize optical signals to transmit information among various items of optical equipment that are coupled to the systems. The system utilize optical fiber cables for transmitting the carrier waves from one item of equipment to another. For example, an optical communications system may comprise a computer central processing unit (CPU), a workstation, a peripheral, such as a printer, each of which is equipped with optical transmitting and receiving devices, and optical fiber cables linked among the CPU, the workstation and printer.
Each item of optical equipment is coupled to the optical fiber cables by means of an optical connector to allow a means of disconnecting the equipment from the optical fiber cables. Such systems may utilize two optical fibers, one for receiving optical signals from an item of optical equipment, and another for sending optical signals. Each optical transmitter has an optical emitter for sending the signals, and each optical receiver has an optical detector for receiving the signals.
Testing of such items of optical equipment is a necessity to assure proper design. In testing, the test conditions must accurately simulate the anticipated operating environment.
In operation, systems of optical fiber cables experience attenuation, which is loss of the transmitted optical power. Such systems, utilizing optical fiber cables and other components, are specified in terms of the maximum optical attenuation that can occur between the transmitting and receiving devices, while still providing information transfer with substantially no errors. Typically, testing of such systems is done by simulation whereby the emitter and detector of the item of optical equipment to be tested are connected to a device that simulates the optical system, including its characteristic attenuation, and the operation of the item is tested as though the item were coupled into the system itself and not to the testing device.
First simulators were devices capable of generating special test signals. Testing was performed externally on the item of equipment being tested. Recently, optical equipment has been designed with internal testing capabilities. With self-testing, the expense of specialized testing equipment and associated testing procedures has been substantially reduced. In place of long lengths of cabling to simulate actual operations and in place of simulators that are devices that produce complex signals or measurements, are simplified simulators comprising internal attenuating devices such as the simplified loop-back attenuator. It is anticipated that such simulation will be used primarily as a simplified and inexpensive means of diagnosing and localizing failures in complex systems of installed equipment.
The present invention relates to simulators which are loop-back attenuators, defined as simulators providing a communication signal path that forms a loop from the emitter to a detector of the same item of optical equipment such that optical signals transmitted from the item under test are looped back to the same item and internally transmitted among its component parts. Consequently, communications from a transmitter to a receiver within the unit of equipment can be accomplished without operation of other units of equipment. Functionality of the optical transmitter and receiver, as well as all electronic circuitry used to generate the required optical signals, can be quickly determined. Simulators which are loop-back attenuators purposely simulate a loss of signal intensity expected of a communications system in which the item may be installed for "on-line" operation. Vastagh, U.S. Pat. No. 4,736,100, discloses a known loop-back attenuator involving an optical fiber cable formed in a loop and having ends of the fiber connected with alignment ferrules. The loop is installed in an alignment fixture that aligns the ends of the loop with the emitter and detector of the item to be tested.
This known loop-back attenuator suffers from disadvantages, mainly being incapable of accurately duplicating the amount of attenuation in the operations system so that the testing device creates an environment approximating the operation of the actual system for meaningful test results. Additionally, results can significantly vary from one type of transmitting or receiving device to another since there is no coupling and confinement mechanism similar to that which the optical emission will encounter in actual use.
Objects of the present invention include providing a simulator in the nature of a loop-back attenuator that, in a compact device, is capable of reproducing the total attenuation of a substantially larger cable network. Other objects include providing a device capable of sufficiently attenuating optical power between emitter and detector of a transceiver or the like, to prevent saturation of the detector, and providing a device which easily and accurately may be controllably altered to match the particular amount of attenuation desired to simulate actual environmental operating conditions or to meet manufacturer's standards.
Other problems associated with known attenuators include that they are expensive to manufacture. The optical fiber forming the loop of the attenuator is held in plastic ferrules within alignment fixtures. The alignment fixtures are secured within a molded casing which comprises a molded upper cover and a molded lower cover. The covers snap together to form, along with the encompassed fiber and alignment fixtures, the optical simulators of the prior art. The separate manufacture of each part of the optical simulator and the process of putting the parts together involves expenses that oftentimes result in an article that is too costly to compete in the market. More economical would be a one-step construction process. Another object of the present invention is to provide a simulator in the nature of a loop-back attenuator which may be simply and economically manufactured by a one-step molding process.
In another aspect of this invention, cost is reduced by use of the loop-back attenuators of the present invention in that the fibers utilized in the body of the simulator may be "gang" polished. That is, the ends of the fibers utilized in the present invention may be polished together to prepare the ends for connection to corresponding optical emitters or detectors. This could not be done with previous devices because the fiber ends were too brittle to withstand the rigors of a gang polish and each end had to be separately polished.
These and other objects are achieved by the simulator of the present invention which is a loop-back attenuator molded into a single body along with a metalized fiber formed into the loop-back. The molded body with metalized fiber provides transmitter to receiver optical loop-back having either low loss or some specified insertion loss value. The metalized glass fiber permits robust capturing of the fiber for proper alignment with other terminated fibers or transmitting and emitting devices in that the metalized glass fiber can be directly overmolded in a single-step manufacturing procedure. Included within the loop-back attenuator is a mechanism that will impart attenuation such as core diameter mismatch. Or the metalized fiber may be modified with structures such as filters or films or the like, and so modified to a precise or exact degree so as to provide a precision attenuation.
The optical simulator is shaped to be interchangeable with the complimentary connector that intermates with an optical connector having an optical emitter and an optical detector. The optical simulator comprises an alignment fixture with connectors for intermating with the optical emitter and the optical detector. Further, the simulator includes an optical fiber formed in a loop and installed within the alignment fixture with a first end face of the loop aligned with the emitter. A second end face of the loop is aligned with the detector of the optical connector. The optical simulator comprises a solid molded body of an electrically insulating material. The optical fiber formed in a loop comprises an optical fiber having an initial thin electroless coating of uniform thickness and a further relatively thick electroplated coating of uniform thickness.
The optical simulator is produced by a process comprising depositing a thin, rigid coating of metal by electroless-plating and a relatively thick electroplated coating to an optical fiber. The optical simulator is then formed in a one-step molding process together with the plated optical fiber to produce an alignment fixture with connectors for intermating with an optical emitter and an optical detector. The metalized fiber loop-back is then modified with a mechanism that imparts attenuation such as core diameter mismatch or with structures such as filters or films, or the like, to produce an improved simulator which is sturdy and inexpensively made.
A number of the simulators may be arranged to present a gang of ends of the metalized fibers forming the loop-backs to permit gang polishing without destroying the physical integrity of the glass fiber structure. Additionally, metalization of the fiber permits the fiber to be subjected to a molding process without harming its integrity where heretofore such molding process would destroy the fiber, if not properly prepared, or would involve a substantial amount of cost in preparing the fiber for such molding.